Control loops are used extensively in electronic circuits to monitor and control various values by controlling or regulating electrical quantities, such as currents and voltages. For example, the current through the stator windings of a polyphase direct current ("dc") motor may be controlled using various control loops that regulate the current through the windings during a particular state or commutation.
At certain times and during certain conditions, control loops may lose control and can no longer regulate or control a particular electrical quantity such as a current or voltage. This loss of control may result in undesirable or unpredictable circuit behavior that prevents a circuit from operating as desired. Sometimes, this loss of control can cause a system to completely fail if corrective action is not taken. Problems are further increased when the loss of control of a control loop goes undetected for a period of time.
Oftentimes, the loss of control by a particular control loop, if known, may signify the end of a particular state or event and trigger the initiation of another circuit or control loop to further control or regulate an electrical quantity. If this loss of control is not quickly detected or goes undetected for too long a period of time, overall system performance suffers as other circuits, such as control circuits, cannot be timely implemented. For example, when a commutation occurs in the stator windings of a polyphase direct current motor, current is switched off through one coil and switched on in another coil. The current through the stator winding coils is controlled using control loops having current feedback. Once a current through a coil is switched off, the control loop loses control and the current should be maintained at zero to enhance overall motor performance. Problems arise when the control loop attempts to further control the current through the coil resulting in an undesirable current through the coil.